Electronic ballasts for operating low-pressure discharge lamps are known in many embodiments. They generally contain a rectifier circuit for the purpose of rectifying an AC voltage supply and charging a capacitor, often referred to as a smoothing capacitor. The DC voltage applied to this capacitor serves the purpose of supplying an inverter which operates the low-pressure discharge lamp. In principle, an inverter produces a supply power for the lamp from a rectified AC voltage supply or a DC voltage supply, said supply power having a much higher frequency than the system frequency. Similar devices are also known for other types of lamps, for example in the form of electronic transformers for halogen lamps.
Dimming devices for operating electronic ballasts for the purpose of controlling the brightness of low-pressure discharge lamps are known per se.
A known possibility for brightness control in this case consists in the lamp power and thus the lamp brightness being adjusted by means of regulating the amplitude of the lamp current. This can take place by bringing the operating frequency of the inverter closer to or further away from resonant frequencies of the lamp/inverter system.